The investigators will use a 2 × 2 × 2 factorial design to investigate the effects of two different doses of vitamin D (10 µg and 25 µg) in children with dark and light skin color, living in northern (Umeå) and southern (Malmö), Sweden. In order to achieve a moderate difference between groups (effect size 0.25) requires 20 children per group (power>87%, alpha = 0.05). With this group size, we can see a group difference in the S-25 (OH) D of 3.75 nmol/L, S-PTH of 0.35 mmol/L and bone mineral density in the lumbar region of 0.075 g/cm2. In Skåne, but not Umeå also a placebo group will participate. With an estimated dropout of 10%, a total of 220 children will be included.